This invention relates to a television tuning system and more particularly to a system for supplying a tuning voltage to a voltage tunable tuner.
A tuning system which provides for the selection of any one of a plurality of television channels in a plurality of bands of radio frequencies is disclosed in my copending application Ser. No. 476,081, filed concurrently herewith and entitled, "Random Channel Address Crystal-Lock Tuning System." To access a given channel, data representative of the channel selected is inserted into a memory, and a reset pulse is generated which initiates a sweep of a voltage controllable tuner through a first of the several frequency bands. As the frequency of an oscillator of the tuner is swept, the oscillator signal is compared to a plurality of harmonically related frequency samples. A counter accumulates a count representative of the number of predetermined frequency difference conditions encountered between the oscillator and the harmonically related samples during a period of sweeping. When the data in the memory equals the count in the counter, a hold signal is developed which stops the sweeping of the tuner. If the data in the memory does not equal the count in the counter at the completion of the sweep of the first band of frequencies, a sweep of the second band of frequencies is initiated, and so on, until the data in the memory equals the count in the counter.
In order that the tuning system function as mentioned above, a tuner frequency controller is provided which generates a tuning voltage which can be swept through a range of voltages in the absence of a hold signal and can be reset for resweeping the range of voltages. In addition, the tuner frequency controller provides for an alteration of the tuning voltage in accordance with an automatic fine tuning (AFT) voltage in the presence of a hold signal. This alteration of tuning voltage with AFT signal compensates for various degrees of overshoot of the optimum tuning voltage due to variations in time required to terminate a sweep and for other component and environmental variations after initially arriving at an optimum tuning voltage.